The HTP is a trimmable component of the aircraft which rotates around an axis fitted to a rear spar of the HTP torsion box. Trimming of HTP is produced frequently during a normal flight, although not always the movement goes from the upper to the lower extreme positions, but small movements are normally produced during the entire flight. The result of that is the electrical harnesses installed at the HTP, are frequently moved with the HTP and therefore they are flexed continuously during the aircraft operative life.
It is also important to minimize the length of the harness to reduce their weight and cost. For that reason, traditionally harnesses at the rear section of an aircraft are fixed to a frame close to the rear spar where the rotation axis is located, and from there the harness passes through the rear spar to the HTP interior. This traditional location of the harnesses at the rear spar, is preferred because it is the nearest location to the rotation axis of the HTP where the relative movement between components is minimal, and as consequence, the length of dynamic harnesses at this area is also minimal.
On the other hand, it is known that electrical dynamic harnesses behave properly with flexion but not so good with torsion efforts. Therefore, as general rule, when a harness is placed in a dynamic area, like for instance a trimmable HTP, it shall be installed such as it is flexed on the same plane. In this way, when the harness is moved, it is maintained on the same plane such as the harness, and therefore the cables housed in it, are subjected only to a flexion effort.
A harness is formed by a plurality of cables enclosed by an electromagnetic (EMI) protection, and all together housed within a protective sleeve. It is essential to assure that none of the harness components would be damaged due to fatigue, during the entire operational life of the aircraft. The EMI protection is a delicate component because it is formed by a lot of thin metallic interwoven metallic strands, which can be broken easily as a result of fatigue.
Taking into account this premise (dynamic movement of harnesses produced on same plane), it is necessary that the attachment points between the harness and the aircraft structure, are keep on same plane so that the path described by the dynamic harnesses is perpendicular to the rotation axis. This concept is illustrated in FIG. 1.
FIG. 1 shows a pair of harnesses, left and right harness (5a,5b) running across the interior of an HTP (2) and passing respectively through left and right rear spars (8a,8b). Left and right harness (5a,5b) have respectively first and second attachment points (5a1,5a2),(5b1,5b2), wherein the first attachment points are fixed to a fuselage frames.